325 research outputs found
Ferruccio Ritossa’s scientific legacy 50 years after his discovery of the heat shock response: a new view of biology, a new society, and a new journal
The pioneering discovery of the heat shock response by the Italian scientist Ferruccio Ritossa reached maturity this year, 2012. It was 50 years ago that Professor Ritossa, through an extraordinary combination of serendipity, curiosity, knowledge and inspiration, published the first observation that cells could mount very strong transcriptional activity when exposed to elevated temperatures, which was coined the heat shock response. This discovery led to the identification of heat shock proteins, which impact many areas of current biology and medicine, and has created a new avenue for more exciting discoveries. In recognition of the discovery of the heat shock response, Cell Stress Society International (CSSI) awarded Professor Ritossa with the CSSI medallion in October 2010 in Dozza, Italy. This article is based on a session of the Fifth CSSI Congress held in Québec commemorating Professor Ritossa and his discovery
EC-SNe from super-AGB progenitors: theoretical models vs. observations
Using a parametric approach, we determine the configuration of super-AGB
stars at the explosion as a function of the initial mass and metallicity, in
order to verify if the EC-SN scenario involving a super-AGB star is compatible
with the observations regarding SN2008ha and SN2008S. The results show that
both the SNe can be explained in terms of EC-SNe from super-AGB progenitors
having a different configuration at the collapse. The impact of these results
on the interpretation of other sub-luminous SNe is also discussed.Comment: Accepted for publication in ApJ
The Possible White Dwarf-Neutron Star Connection
The current status of the problem of whether neutron stars can form, in close
binary systems, by accretion-induced collapse (AIC) of white dwarfs is
examined. We find that, in principle, both initially cold C+O white dwarfs in
the high-mass tail of their mass distribution in binaries and O+Ne+Mg white
dwarfs can produce neutron stars. Which fractions of neutron stars in different
types of binaries (or descendants from binaries) might originate from this
process remains uncertain.Comment: 6 pages. To appear in "White Dwarfs", ed. J. Isern, M. Hernanz, and
E. Garcia-Berro (Dordrecht: Kluwer
Supernova rates from the Southern inTermediate Redshift ESO Supernova Search (STRESS)
To measure the supernova (SN) rates at intermediate redshift we performed the
Southern inTermediate Redshift ESO Supernova Search (STRESS). Unlike most of
the current high redshift SN searches, this survey was specifically designed to
estimate the rate for both type Ia and core collapse (CC) SNe. We counted the
SNe discovered in a selected galaxy sample measuring SN rate per unit blue band
luminosity. Our analysis is based on a sample of ~43000 galaxies and on 25
spectroscopically confirmed SNe plus 64 selected SN candidates. Our approach is
aimed at obtaining a direct comparison of the high redshift and local rates and
at investigating the dependence of the rates on specific galaxy properties,
most notably their colour. The type Ia SN rate, at mean redshift z=0.3, amounts
to 0.22^{+0.10+0.16}_{-0.08 -0.14} h_{70}^2 SNu, while the CC SN rate, at
z=0.21, is 0.82^{+0.31 +0.30}_{-0.24 -0.26} h_{70}^2 SNu. The quoted errors are
the statistical and systematic uncertainties. With respect to local value, the
CC SN rate at z=0.2 is higher by a factor of ~2 already at redshift, whereas
the type Ia SN rate remains almost constant. This implies that a significant
fraction of SN Ia progenitors has a lifetime longer than 2-3 Gyr. We also
measured the SN rates in the red and blue galaxies and found that the SN Ia
rate seems to be constant in galaxies of different colour, whereas the CC SN
rate seems to peak in blue galaxies, as in the local Universe. SN rates per
unit volume were found to be consistent with other measurements showing a
steeper evolution with redshift for CC SNe with respect to SNe Ia. Finally we
have exploited the link between star formation (SF) and SN rates to predict the
evolutionary behaviour of the SN rates and compare it with the path indicated
by observations.Comment: Accepted for publication in A&A; 25 pages (including on line
material), 13 figure
Evolution of the number of accreting white dwarfs with shell nuclear burning and of occurrence rate of SN Ia
We analyze temporal evolution of the number of accreting white dwarfs with
shell hydrogen burning in semidetached and detached binaries. We consider a
stellar system in which star formation lasts for 10 Gyr with a constant rate,
as well as a system in which the same amount of stars is formed in a single
burst lasting for 1 Gyr. Evolution of the number of white dwarfs is confronted
to the evolution of occurrence rate of events that usually are identified with
SN Ia or accretion-induced collapses, i.e. with accumulation of Chandrasekhar
mass by a white dwarf or a merger of a pair of CO white dwarfs with total mass
not lower than the Chandrasekhar one. In the systems with a burst of star
formation, at 10 Gyr observed supersoft X-ray sources, most probably, are
not precursors of SN Ia. The same is true for an overwhelming majority of the
sources in the systems with constant star formation rate. In the systems of
both kinds mergers of white dwarfs is the dominant SN Ia scenario. In symbiotic
binaries, accreting CO-dwarfs do not accumulate enough mass for SN Ia
explosion, while ONeMg-dwarfs finish their evolution by an accretion-induced
collapse with formation of a neutron star.Comment: 11 pages, 2 figures, accepted by Astronomy Letter
Description of the Scenario Machine
We present here an updated description of the "Scenario Machine" code. This
tool is used to carry out a population synthesis of binary stars. Previous
version of the description can be found at
http://xray.sai.msu.ru/~mystery//articles/review/contents.htmlComment: 32 pages, 3 figures. Corrected typo
SN 2008S: an electron capture SN from a super-AGB progenitor?
We present comprehensive photometric and spectroscopic observations of the
faint transient SN 2008S discovered in NGC 6946. SN 2008S exhibited slow
photometric evolution and almost no spectral variability during the first nine
months, implying a high density CS medium. The light curve is similar in shape
to that of SN 1998S and SN 1979C, although significantly fainter at maximum
light. Our quasi-bolometric lightcurve extends to 300 days and shows a tail
phase decay rate consistent with that of ^{56}Co. We propose that this is
evidence for an explosion and formation of ^{56}Ni (0.0015 +/- 0.0004 M_Sun).
The large MIR flux detected shortly after explosion can be explained by a light
echo from pre-exisiting dust. The late NIR flux excess is plausibly due to a
combination of warm newly-formed ejecta dust together with shock-heated dust in
the CS environment. We reassess the progenitor object detected previously in
Spitzer archive images, supplementing this discussion with a model of the MIR
spectral energy distribution. This supports the idea of a dusty, optically
thick shell around SN 2008S with an inner radius of nearly 90AU and outer
radius of 450AU, and an inferred heating source of 3000 K and luminosity of L ~
10^{4.6} L_Sun. The combination of our monitoring data and the evidence from
the progenitor analysis leads us to support the scenario of a weak electron
capture supernova explosion in a super-AGB progenitor star (of initial mass 6-8
M_sun) embedded within a thick CS gaseous envelope. We suggest that all of main
properties of the electron capture SN phenomenon are observed in SN 2008S and
future observations may allow a definitive answer.Comment: accepted for publication in MNRAS (2009 May 7
Differential Levels of Stress Proteins (HSPs) in Male and Female Daphnia magna in Response to Thermal Stress: A Consequence of Sex-Related Behavioral Differences?
In two independent experiments, we compared: (1) water depth selection (and accompanying temperature selection) by male and female Daphnia magna under different kinds of environmental stress, including the presence of filamentous cyanobacteria, the risk of predation from fish, and the presence of toxic compounds; and (2) sex-dependent production of heat shock proteins (HSP60, 70, and 90) in response to a sudden change in temperature. Male D. magna selected deep water strata, which offer a relatively stable environment, and thereby avoided the threat of predation and the presence of toxic compounds in surface waters. Correlated with this behavior, males reduce their molecular defenses against stress, such as the production of heat shock proteins (HSPs), and do not maintain the physiological machinery that triggers an increase in HSP levels in response to stress. In contrast, female D. magna actively select habitats that offer optimal conditions for growth and production of offspring. Consequently, females are exposed to variable environmental conditions that may be associated with increased stress. To permit survival in these different habitats, D. magna females require molecular mechanisms to protect their cells from rapid changes in stress levels. Thus, they maintain high constitutive levels of the heat shock proteins from HSP 60, 70, and 90 families, and they have the potential to further enhance the production of the majority of these proteins under stress conditions. The results of this study indicate that the separate habitats selected by male and female D. magna result in different patterns of HSP production, leading us to hypothesize that that male and female Daphnia magna adopt different strategies to maximize the fitness of the species
From the CMD of Omega Centauri and (super-)AGB stellar models to a Galactic plane passage gas purging chemical evolution scenario
[Abbreviated] We have investigated the color-magnitude diagram of Omega
Centauri and find that the blue main sequence (bMS) can be reproduced only by
models that have a of helium abundance in the range Y=0.35-).
Y~0.35 must also be assumed in order to counteract the effects of high CNO on
turnoff colors, and thereby to obtain a good fit to the relatively blue turnoff
of this stellar population. This suggest a short chemical evolution period of
time (<1Gyr) for Omega Cen. Our intermediate-mass (super-)AGB models are able
to reproduce the high helium abundances, along with [N/Fe]~2 and substantial O
depletions if uncertainties in the treatment of convection are fully taken into
account. These abundance features distinguish the bMS stars from the dominant
[Fe/H] population. The most massive super-AGB stellar models
(M_zams>=6.8M_sun, M_He,core>=1.245M_sun) predict too large N-enhancements,
which limits their role in contributing to the extreme populations. We show
quantitatively that highly He- and N-enriched AGB ejecta have particularly
efficient cooling properties. Based on these results and on the reconstruction
of the orbit of Omega Cen with respect to the Milky Way we propose the galactic
plane passage gas purging scenario for the chemical evolution of this cluster.
Our model addresses the formation and properties of the bMS population
(including their central location in the cluster). We follow our model
descriptively through four passage events, which could explain not only some
key properties of the bMS, but also of the MS-a/RGB-a and the s-enriched stars.Comment: Accepted for publication in ApJ. 10 figures, 5 tables, 21 page
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